I had the same problem when my son and dil got a queen and I was making for a double! I simply added more borders, one smaller one and one larger. Your 8-10 inch one should be Ok on a king size bed. How big are your blocks? Usually that governs how big my borders are. Your large border might be better as 2 smaller, say a 4 and a 6 inch OR a 3 and a 7. Clear as mud?